This invention is concerned with medical diagnostic imaging systems, and more particularly with computerized tomographic (CT) systems, particularly such systems used for clinical screening of patients and potential patients.
The present invention pertains to CT scanning systems utilizing X-ray radiation for generating images of the interior regions of human patients. It will be appreciated by those skilled in the art that the present invention will also find application in conjunction with industrial CT systems used for quality assurance and the like.
In general, CT systems comprise an X-ray source and X-ray detectors for detecting the X-rays after they have passed through a subject or object. The X-ray source and associated detectors, in what are known as third generation CT systems, rotate together around the subject. In what are known as fourth generation CT systems, the X-ray source rotates about the subject being examined while the detectors are stationary and surround the subject being imaged.
In the past, CT systems have been used for detailed studies of symptomatic and sickly patients. However, to a greater extent than ever, examinations referred to as screening examinations are made for asymptomatic and healthy patients on the theory that an ounce of prevention is worth a pound of cure. Thus, if malfunctioning of an organ in a patient can be detected in its very early stages, then a complete cure is much more likely. To provide the capability of detecting health problems in early stages, the images have to be sufficiently detailed to indicate health problems. Accordingly, screening examinations ideally should provide for acquiring 2-dimensional and 3-dimensional images using helical scans.
Presently, in general, systems that provide helical scanning, use X-ray sources that traverse the patient horizontally. That is, the patient is disposed horizontally on a patient support such as a bed, and the X-ray source rotates about the patient and the bed while the bed moves horizontally. The necessity of rotating around the patient plus the bed increases the size of the system. In addition, the source and associated paraphernalia are operating against gravity for a large portion of each rotation and thus the system requires more power and sturdier components, all of which increase the size and cost of the CT systems.
Presently, there are no CT systems available that are designed primarily for screening and nonetheless provide helical scanning. An ideal screening system should be relatively small and inexpensive, and therefore should ideally fit into medical centers and clinics where most of the screening examinations take place. To assure maximizing the discovery of latent health problems, the CT screening apparatus should be capable of conducting helical scans.
Of course, any CT system that is reduced in size and capable of conducting scanning, including helical scanning, whether or not it is sufficiently inexpensive for screening, would be useful.
The system described herein provides helical scans in a vertical direction. Scanning systems, wherein the scanning apparatus is positioned by vertical movement, have been known in the past. However such scanning systems did not teach or make obvious the use of vertical scanning, and certainly not for providing helical scans in a simple and elegant manner. Vertical positioning for CT scans are shown, for example, in PCT application US90/05821, published under publication no. WO91/07131, and the contents of that application are hereby incorporated herein by reference. This prior art device uses the vertical movement capabilities of the scanner to position the scanner to obtain a CT image of a desired location in the patient, not for continuous scanning during vertical movement. No movement takes place during the scanning.
An example of a prior art, inexpensive CT X-ray scanner, is to be found in U.S. Pat. No. 4,829,549. However, the scanner of that patent does not do a whole body scan. It is designed to image the limbs or parts of limbs of patients and is primarily used for detection of osteoporosis. The vertical motion of the scanning parts of the system of the patent are for positioning the scanning components, and no movement takes place during scanning.
Vertical scanning is shown in U.S. Pat. No. 5,305,363. However, that patent teaches the use of a unique X-ray source, in the form of a toroidial tube. The patent does teach helical scanning, when the scan is in the horizontal direction, but it fails to teach helical scanning when the scan is in the vertical direction. More particularly, since the object of the present invention is to provide an inexpensive CT system, the ""363 patent teaches in an opposite direction; since it actually provides a more expensive CT system with its unique toroidial X-ray source, which accordingly would not be at all economic for screening.
An aspect of some preferred embodiments of the present invention is to provide a smaller, but extremely efficient CT system that can be used, among other things, for screening. To reduce the size and cost of the CT system, the patient support or bed normally associated with the CT scanner is eliminated, and vertical scanning is used.
According to an aspect of some preferred embodiments of the present invention, the CT scanning system includes a gantry or CT ring that contains an X-ray source and oppositely disposed detector apparatus. The subject either sits or stands in the center of the ring, and the ring moves vertically while rotating about the patient to provide the helical scans. According to an aspect of the invention, the helical scanning movements, both vertical and rotational, are done by the source and associated detectors.
In an aspect of some preferred embodiments of the invention, a small, inexpensive X-ray tube power supply is used. It is trickle-charged between patients and discharged during the scan. The high-voltage cable, on systems using such a power supply, does not have to be flexible, since the charged power supply is mounted directly upon rotating, vertically moving CT ring. Thus, the high-voltage cable that trickle-charges the high-voltage power supply is disconnected during the actual scan and only connected between scans.
In an aspect of some preferred embodiments of the invention, view data are recorded in a memory on the moving gantry during the scan, thereby eliminating the need for expensive data transmission apparatus. The memory, such as a hard disc, is replaced between patients or can be read out between patients, and reconstruction is carried-out on a separate console. The separate console can be used for a multiplicity of scanners, or the separate console can be used for the regular patients in the hospital during the day, and used for the screening of patients in the evening.
In another preferred embodiment, the system is installed in a mobile screening vehicle, and the image is reconstructed and evaluated at a central public health clinic, where a single sophisticated processing work station may be installed to serve a multiplicity of such mobile units.
Accordingly, preferred embodiments provide a CT system that is inexpensive, occupies a small space and is light in weight, but is capable of effective helical scanning. These advantages make it ideal for screening using multiple stations or for use as a mobile unit.
In accordance with a preferred aspect of the invention, a computerized tomographic imaging system is provided, which includes a gantry or CT ring defining a central bore surrounding the subject being imaged. At least one X-ray source is mounted on said gantry for emitting X-rays. X-ray detectors are also mounted on the gantry, oppositely disposed from said at least one X-ray source, to detect X-rays that have traversed said subject The gantry moves on vertically-extending, helically-arranged rails, causing the X-ray source to describe a helix to provide a helical scan of the subject, as the gantry travels over the vertically-extended, helically-arranged rails. Alternatively, the gantry moves vertically while the at least one X-ray source rotates about the patients to provide helical scans.
In third generation systems, detectors are mounted opposite the at least one X-ray source and arranged to rotate with the at least one X-ray source about the subject. In fourth generation systems, only the at least one X-ray source rotates. Detectors are mounted on the gantry surrounding the subject.
In a preferred embodiment of the invention, the detectors, which within the scope of the invention may be single slice, multi-slice or large area detectors, acquire imaging data during said helical scan. An image reconstructor is provided for reconstructing images from said imaging data, and display means display the reconstructed images.
There is thus provided in accordance with a preferred embodiment of the invention a computerized tomographic (CT) imaging system comprising: a gantry defining a central bore surrounding an object being imaged; at least one X-ray source mounted on the gantry for emitting X-rays; X-ray detectors mounted on said gantry to detect X-rays from said source that traverse said object; and a helical movement arrangement for moving the gantry vertically while rotating the at least one X-ray source about the object being imaged to provide a helical scan. In a preferred embodiment of the invention, the at least one X-ray source is affixed to said gantry; and the helical movement arrangement includes vertically extending helically-arranged rails to provide a helical scan of the subject as the gantry travels over the rails. Preferably, the arrangement further includes coupling units attached to said gantry for coupling said gantry to said rails. Preferably, the arrangement includes a rack on said rails and wherein said coupling units include gears meshing with said rack. In a preferred embodiment, the gears are motorized. Preferably, the detectors are arranged to acquire imaging data during said helical scan.
Preferably, the arrangement includes: a vertical movement arrangement for moving said gantry with said at least one X-ray source vertically; and a rotating movement arrangement wherein the at least one X-ray source rotates within said gantry about said object while said gantry is moving vertically. Further, preferably the X-ray detectors are fixedly mounted opposite said at least one X-ray source to receive X-rays that have traversed the object and to move with said at least one X-ray source. In a preferred embodiment of the invention, an image constructor that reconstructs images from said imaging data; and a monitor is also provided that displays said reconstructed images.
In a preferred embodiment of the invention, the CT imaging system includes a memory that receives said acquired image data to enable the provision of images at a central imaging data processing and display center. Preferably, the said memory is located on the gantry. Further, preferably a power pack is mounted on said gantry for powering the components on said gantry during the helical scan. Still further, preferably the power pack includes high voltage capacitors. Preferably, a trickle charger for charging said power pack when not in use is provided. Preferably, the capacitors are in parallel during the charging and in series during use.
In a preferred embodiment of the invention, the at least one X-ray source includes more than one X-ray source mounted on said gantry. Preferably, the at least one X-ray source comprises a single focal spot X-ray source. Alternatively, the at least one X-ray source includes multiple focal spots.
In a preferred embodiment of the invention, the X-ray detectors comprise a single row of X-ray detectors. Alternatively, the X-ray detectors comprise multiple rows of detectors. Preferably, the X-ray detectors comprise area detector arrays.
There is further provided a method for providing computerized tomographic (CT) images comprising: directing X-ray beams at an object; detecting X-ray beams that have traversed the object; and moving the X-ray beams vertically while rotating about the object being imaged to provide a helical scan. Preferably, the X-ray beams are moved along a set helical path. Preferably, the X-ray beams are rotated while moving them vertically to describe a helical scan. Still further, preferably gravity is used to move the X-ray beams. Alternatively or additionally, preferably motorized equipment to move the X-ray beams.
In a preferred embodiment of the invention, imaging data are acquired during said helical scan Preferably, images are reconstructed from the imaging data; and the reconstructed images are displayed. Preferably, the image data are converted to memory and used to generate images at a central imaging data processing and display center.
In a preferred embodiment of the invention, a single focal spot X-ray source is used for directing X-rays at an object. Alternatively, a multiple focal spot X-ray source is used for directing said X-ray beams at an object Preferably, X-ray detectors that comprise a single row of X-ray detectors are provided. Further, preferably X-ray detectors that comprise multiple rows of detectors are used. Alternatively, large area detector arrays are provided.